Australasian Science: Australia's authority on science since 1938

Does Fishing Kill Fish?

By Hugh Possingham

Do marine reserves work?

Science has long demonstrated that marine reserves protect marine biodiversity. Rather than answer the same question again, isn’t it about time we started funding research that answers some useful scientific questions?

As marine reserves spread inexorably across the planet, the cry from skeptics and some fishermen is: “Do marine reserves work?” The science is pretty clear but acknowledgement of this by the public is another story. Let me begin with a story of my experience answering this question while communicating to stakeholders the subtleties of marine conservation planning during the rezoning of Moreton Bay.

I was asked by the then-Queensland Environmental Protection Agency to explain to stakeholders the process of marine reserve system design as it applied to the Moreton Bay rezoning. I told the gathering that the rezoning was about conserving a fraction of each mappable biodiversity attribute (species and habitats) for the minimum impact on the livelihood of others.

Things were going well (I thought), but then came the first question: “Prove to us marine reserves work! I don’t think they do.”

When I asked why he felt this way he responded: “Because most of the fish we catch move so much we will catch them when they come out of the reserve”.

I responded (though not quite this eloquently): “Your argument leads to two logical responses – there is no case for compensating fishermen for the new marine reserves in Moreton Bay because you catch the fish when they come out, or the reserves need to be a lot bigger”.

I went on to say: “Furthermore we have proved that marine reserves work in at least 100 studies worldwide. Why wouldn’t they work in Moreton Bay?” But the response from the fishing stakeholders was: “We need it proved that they work in Moreton Bay. Moreton Bay is different.”

Around Australia, as our governments boldly forge ahead rezoning Australia’s waters, the question of whether marine reserves work is asked by many people who do not know the marine literature. As a result a great deal of monitoring and evaluation effort is being spent on testing the null hypothesis: “Fishing does not kill fish”.

The classic Honours student Before-After-Control-Impact (BACI) design is being rolled out across Australia, and it looks a bit like this: we count and measure fish in several places, stop fishing in some of those places, continue to count and measure so we can try to reject the null hypothesis that fishing has no impact.

Sometimes we can’t prove it, because we don’t have enough data. However, an alternative approach is to go to the local primary school and ask a small child: “If we stop killing all the fish in a place do you think there may be more of them and the ones left may be bigger?”

Of course there are many subtleties to the removal of fishing pressure – in more sedentary species territorial adults may exclude juveniles and numbers may drop. For some species reserves will be too small, and if we have reserve size as a covariate then we might get useful information about minimum reserve size.

However, when you establish a protected area, invariably biomass (the combination of numbers and size) will go up, especially in the higher trophic levels. You can’t remove lots of fish without having an impact – to ask this question again and again is like questioning the powers of gravity every day in every place. Next time you fly to New Zealand be careful when you step out of the plane in case gravity failed while you were crossing the Tasman.

Just because policy-makers, stakeholders, managers or politicians ask a question it doesn’t mean that scientists should take funding to answer it. Ecology may be a difficult science with few fundamental laws, but many of its laws and principles are global – like killing animals reduces population size.

There are useful scientific questions we can answer while monitoring marine reserves that will help with future rezoning and policy. The key is that applied monitoring has to pass some tests.

Do we know enough already from other studies? Is the answer already obvious? If we get an answer do we have a management response?

This sort of thinking will be the subject of some of the research of the new ARC Centre of Excellence for Environmental Decisions, which gets underway this year. Watch this space!

Professor Hugh Possingham is Director of the Applied Environmental Decision Analysis centre at the University of Queensland.